Thus the lever only _gathers_ or _concentrates_ force, as it were, but does not at all increase it.
It is so with all the other contrivances for managing force for the accomplishment of particular purposes.

None of them, increase the force, but only alter its form and character, with a view to its better adaptation to the purpose in view.
Nor can any force be extinguished.

When a bullet strikes against a solid wall, the force of its movement, which seems to disappear, is not lost; it is converted into heat--the temperature of both the bullet and of that part of the wall on which it impinges being raised by the concussion.

And it is found that the amount of the heat which is thus produced is always in exact proportion to the quantity of mechanical motion which is stopped; this quantity depending on the weight of the bullet, and on the velocity with which it was moving.

And it has been ascertained, moreover, by the most careful, patient, and many times repeated experiments and calculations, that the quantity of this heat is exactly the same with that which, through the medium of steam, or by any other mode of applying it, may be made to produce the same quantity of mechanical motion that was extinguished in the bullet.